There are various types of expanding/contracting conical ring or rings that utilize frictional wedge designs in place of keys or interference forced fit to connect machine elements and transmit torque. An examination of the prior art includes the following:
U.S. Pat. No. 3,957,381 to Schafer discloses a connector that includes a double-cone that produces a highly concentrated contact pressure and slight variations in tightening the clamping screws result in installation concentricity error. Given the number of clamping screws, it was necessary to adhere to a restricted installation tightening procedure. These restrictions resulted in the need for external centering shims or piloted machine elements.
U.S. Pat. No. 4,304,502, to Stratienko describes a connector that provides for a much less contact pressure than Schafer's U.S. Pat. No. 3,957,391, but does not address the problem of installation concentricity error.
U.S. Pat. No. 5,374,135 to Folsom and U.S. Pat. No. 5,474,403 to Hetrich address the known installation difficulty of mounting machine elements with clamping devices that utilize multiple screws. The devices taught by U.S. Pat. Nos. 5,374,135 and 5,474,403 are limited by the relatively low torque capacity that can be achieved by one large nut and their intolerance to bending moment. The common feature of the clamping devices shown by these two patents is that the conical rings and the circumferential webs of the double conical rings have the bores for the tensioning screws and the forcing screws on a common pitch circle and at the same spacings. As a consequence, at some locations on the circumference bores for forcing screws are arranged in the positions in which tensioning screws would normally be located. This design considerably simplifies the production on a drilling unit with corresponding dividing apparatus.
The uniform spacings, while providing advantages in terms of production, nevertheless involve problems regarding the correct installation of the front conical ring, the front conical ring being directed toward the caps of the tensioning screws. The problem of misalignment can occur whether assembly takes place at the factory or on site, e.g. when fastening belt-drive drums for conveying belts in mining or the like. Incorrect installation can easily occur because it is not easy to see, from the front, whether the conical ring is in the correct angular position with respect to the double conical ring. When in the correct position, the various types of bores coincide precisely. In the event of careless installation, the conical surfaces may not coincide, with one of the conical axis being misdirected from being longitudinally parallel. Sometimes the threaded bores in the front conical ring, (the front conical ring being directed toward the caps of the tensioning screws), and the threaded bores for releasing the front conical ring from the double conical ring, are located opposite and in alignment with threaded bores in the circumferential web of the double conical ring which are provided for the release of the conical ring directed away from the caps of the tensioning screws. Since the number of forcing screws for releasing the front conical ring and the rear conical ring are equal and the forcing screws are distributed uniformly over the circumference, all the threaded bores in the front conical ring may be located opposite the threaded bores in the circumferential web.
After the relative positions of the rings have been set, the forcing screws are screwed into the threaded bores of the front conical ring and come into contact with the threaded bores in the circumferential web. As a result, it is more difficult to force off the front conical ring because there is no real abutment to effect the necessary leverage. In addition, the threaded bores in the circumferential web are destroyed such that, in some circumstances, it is no longer possible to force off the rear conical ring and consequently the entire conical tensioning assembly can no longer be released. U.S. Pat. No. 5,269,622 to Mullenberg discusses the problem of releasability, but proposes a structure in which the same screws are used to tighten and loosen the connector.
The prior art discusses the problem of releasing a connector assembly after it has been installed. It may be a number of years before this situation arises, when release of the connector assembly is made more difficult by corrosion and dirt. Accordingly, when such a case does occur, the damage is considerable.
The primary objective of the invention is to overcome the problems of the prior art and provide a self centering keyless bushing capable of transmitting high amounts of torque, thrust and bending moment connection for rotationally and axially securing machine elements where the machine element is drivingly coupled to a shaft. It is also an objective of the present invention to provide a keyless bushing that is simple to install and that is readily releasable.